Study finds weak evidence for garlic in high blood pressure

A vendor removes the skin of garlic at a vegetable wholesale market in Beijing May 10, 2010. REUTERS/Jason Lee

EW YORK (Reuters Health) - A new analysis of past clinical trials using garlic supplements against high blood pressure finds a modest benefit, but researchers urge longer, more rigorous studies to assess the popular alternative “treatment.”

“Many individuals with high blood pressure oppose conventional antihypertensive drugs and are more open to ‘natural’ treatment,” said the study’s senior author Dr. Alain Nordmann, of the Basel Institute for Clinical Epidemiology and Biostatics at the University of Basel in Switzerland.

“There is some evidence that garlic may lower blood pressure in individuals with hypertension in the short-term, but the quality of the studies are not that great and long-term data is missing,” Nordmann told Reuters Health in an email.

Nearly one of every three adults in the United States has high blood pressure, which increases their risk of heart attacks, strokes, heart failure and kidney disease.

Worldwide, high blood pressure, or hypertension, contributes to about half of deaths due to stroke or heart disease, Nordmann and his colleagues write in the American Journal of Hypertension.

A significant portion of people with high blood pressure don’t have it under control, they add, and one reason is that patients often fail to take their medications.

Seeking alternatives to current blood pressure medicines, many people have turned to garlic – usually in the form of dried-garlic capsules – for its supposed blood pressure lowering properties. But only a handful of trials have shown evidence that garlic helps people with hypertension.

Nordmann and colleagues collected data from nine previously published studies that included 482 people with blood pressure readings of at least 140/90 mm Hg, the cutoff for diagnosis of high blood pressure.

All the studies compared garlic with either a placebo or regular care and lasted at least four weeks.

When Nordmann’s team combined the data, they found statistically significant reductions in systolic blood pressure (the top number) by about 9 mm Hg and diastolic blood pressure by about 4 mm Hg when garlic preparations were used.

The authors say the effect was comparable to blood pressure-lowering medications, at least in the short term.

But, they note, most of the studies were small, and their methods were not ideal. In addition, most of the studies used garlic powder, but the dosages ranged from 600 to 2,400 milligrams per day. And some of the studies used fresh garlic instead.

When the review team re-analyzed the results using only the highest quality studies, the effectiveness of garlic was not as strong.

“More than 25 years after the first garlic trial it is about time to conduct ‘the’ definite trial,” Nordmann said. “I assume funding is the problem since no drug company has an interest in a natural product lowering blood pressure.”

Nordmann said that people who are thinking about using garlic should wait until larger, high quality long-term trials are completed before taking garlic.

“If they refuse to take conventional antihypertensive drugs, garlic is an option, but blood pressure must be carefully monitored,” he said.

“I think that they did a very good faith effort to thoroughly evaluate the literature about the potential impact of garlic on blood pressure,” said Dr. Robert Ostfeld, a cardiologist and director of the Cardiac Wellness Program at Montefiore Medical Center in New York.

“And there are some interesting reasons to think that garlic might be helpful for blood pressure in that there are other studies that suggest garlic may improve blood vessel function, and it has antioxidant and anti-inflammatory properties,” said Ostfeld, who was not involved in the new study.

He noted that there are “pluses and minuses” when doing this type of analysis of previous research, including biases in the individual studies, and the authors acknowledge that.

Osfeld agrees with the conclusion that there’s insufficient evidence to have confidence that garlic is an effective therapy for high blood pressure.

“I think honestly the jury is still out,” he said. There’s a physiological rationale to think it might work, but we lack conclusive evidence, he said.

Ostfeld said that for the most part, eating garlic is safe, except for some people who may be taking multiple blood thinners, such as Coumadin. He added that patients on these medications should talk to their doctor before taking garlic.

It’s very important for people to know they should not replace proven therapies for high blood pressure with garlic based on this study, Ostfeld said.

He added that it’s common for people to look for a magic bullet to fix a problem such as high blood pressure.

“I think a magic bullet already exists and that would be a healthier lifestyle - a whole-food, plant-based diet, which garlic can be a delicious addition to, and regular exercise as your medical condition permits,” he said.

“I think the combination of those two things will go a very long way to helping to improve oneself and garlic is a piece of that very, very important puzzle,” Ostfeld said.

SOURCE: bit.ly/1sLlxOb American Journal of Hypertension, online September 18, 2104.